Portable screening apparatus is known by which particulate materials such as rocks and gravel can be screened and sifted for use. Examples of known screening apparatus are shown in U.S. Pat. Nos. 2,922,510 and 3,402,816. In general, such apparatus includes a hopper and an associated grizzly disposed at the lower end of an inclined endless conveyor belt, at the upper end of which is disposed a sifting mechanism which discharges screened material into a truck bin or other receptacle for later use. A load of gravel or other particulate material is dumped upon the grizzly where most of the material will pass through the bars into the hopper for dispensing onto the conveyor belt. Larger objects remaining on the grizzly can be manually or automatically removed. The conveyor belt supplies material to the sifter which provides a sifted load to the truck. Such apparatus is often mounted on wheels, as shown in the above-cited patents, so that the entire rig can be trailed by a truck to an operating site. In the apparatus of U.S. pat. No. 2,922,510, a screening member is foldable during transportation of the apparatus and is adjustably positioned by means of link chains.